Electron Configurations

Outcomes:Write electron configurations for elements of the periodic table. Include: selected elements up to atomic number 36 (Krypton)

Relate the electron configuration of an element to its valence electron(s) and its position on the periodic table.

Electron ConfigurationsWriting the Electron Configuration

• We use a STANDARD NOTATION for writing electron configurations.

• The number includes the PRINCIPAL ENERGY LEVEL (n) of the electron, the NAME of the ORBITAL and the NUMBER of ELECTRONS in that orbital.

• The electron configuration of oxygen is:

Electron Configurations

The electron configuration shows that there are:

• 2 electrons in the s-orbital of the first energy level (1s2)

• 2 electrons in the s-orbital of the second energy level (2s2)

• 4 electrons in the p-orbital of the second energy level (2p4)

NOTE:

The ORBITALS are always written as LOWER CASE letters and the NUMBER of ELECTRONS is always written as SUPERSCRIPTS.

Electron ConfigurationsThe Zig-Zag Rule:• The OVERLAP between d, f, and s-orbitals makes remembering electron configurations

difficult. • Start by writing the orbitals out in a LIST downwards:

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

Electron ConfigurationsThe Zig-Zag Rule:

• We can draw a DIAGONAL LINE through the orbitals.

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

• To write the filling order we just follow the diagonal lines.• When we reach the tip (end) of an arrow, we start at the tail (start) of the next arrow. • The filling order is:

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s ...

Electron ConfigurationsExamples:

Write the electron configuration for the following:

Calcium

Germanium

Neon

Electron ConfigurationsTry these ones…

Write the electron configuration for the following:

Sodium

Magnesium

Aluminum

Noble Gas NotationIf you look at the “try these ones” above, what do you notice?

They all start with 1s22s22p6

We can SHORTEN the electron configuration of an element by using the symbol for the NOBLE GAS before it.

Our try these ones would now look like this: Sodium

Magnesium

Aluminum

In fact, this is how many periodic tables display the electron configurations…

Noble Gas Notation

http://www.mpcfaculty.net/mark_bishop/abbreviated_electron_configuration_help.htm

Electron Configuration of Ions• When writing the valence configurations of IONS you must consider the CHARGE of the ion.

• The charge will determine the NUMBER of ELECTRONS.

• A POSITIVE ion will have FEWER electrons and a NEGATIVE ion will have MORE electrons.

Examples:

Write the electron configurations for the following:

Calcium Ion (Ca2+)

Chloride Ion (Cl-)

Copper(II) Ion (Cu2+)

Valence Electron ConfigurationsValence electrons are found in the outermost energy level, or have the highest principle quantum number (n).

Examples:

Write the valence electron configuration for the following:

Fluorine

Solution…

Step 1. Write the complete electron configuration.

Fluorine = 9 electrons

1s22s22p5

Step 2. Choose the electrons in the highest energy level.

The highest energy level is the second, so the electrons in the second energy level are the valence electrons.

The valence configuration is 2s22p5

Valence Electron ConfigurationsExamples: (Con’t)

Germanium

Solution…

Step 1. Write the complete electron configuration.

Germanium = 32 electrons

1s22s22p53s23p64s23d104p2

Step 2. Choose the electrons in the highest energy level.

The highest energy level is the fourth, so the electrons in the fourth energy level are the valence electrons.

The valence configuration is 4s24p2

NOTE:

Even though the 3d orbital fills after the 4s orbital, the 4s orbital is in the highest or outer-most energy level.

Electron ConfigurationsElectron Configurations and the Periodic Table

In the periodic table below, write the last orbital of each elements configuration in each box. It has been started for you…

Do you notice any trends in the table?

2p2 2p3 2p4 2p5 2p6

3s1 3s2 3p1 3p2 3p3 3p4 3p5 3p6

4s1 4s2 3d1 3d2 3d9 3d10 4p1 4p6

5s1 5s2 4d1 4d2 4d9 4d10 5p1 5p6

Electron ConfigurationsPeriodic Trends

The periodic table seems to be arranged according to the electron configuration of the atoms:

• The electron configuration of atoms in these 4 areas will have the indicated orbital filling LAST. (Ex. transition metals fill the d-orbitals)

• Another trend is the ENERGY LEVEL of the valence electrons is the SAME as the PERIOD of the atom. Note that the 1st period is omitted above.

• We have learned before that elements in COLUMNS or GROUPS have SIMILAR PROPERTIESbecause they have SIMILAR VALENCE electron configurations.

• An element’s chemical PROPERTIES and BONDING characteristics are determined by its VALENCE ELECTRONS.

Electron ConfigurationsPeriodic trends:

Here are a couple of different periodic tables that may help you to determine electron configurations...

Periodic Table with Electron Configs.pdf

s, p, d, f Blocks Table